Method and system for varying the characteristics of a dispersive delay line

ABSTRACT

A method and system are disclosed for selectively varying the phase dispersion characteristic of a dispersive meander line as well as a method and system for employing the variable dispersion characteristics for second harmonic signal suppression in amplifier chains. The dispersive characteristics of the disclosed variable dispersion meander line are varied by selectively changing the ratio between the gap spacing of interacting line segments and the pitch of the interacting line segments. The gap spacing to pitch ratio may be continuously varied within a desired range while maintaining an acceptable characteristic impedance.

United States Patent [1 1 Schellenberg et al.

[ Nov. 19, 1974 OTHER PUBLICATIONS METHOD AND SYSTEM FOR VARYING THE CHARACTERISTICS OF A DISPERSIVE DELAY LINE Tu A Computer-aided Desi gn of a Microwave Delay Equalizer in IEEE Trans. on Microwave Theory and Techniques Vol. MTT-l7, Aug. 1969, pp.

[75] Inventors: James M. Schellenberg, Severna Park; Raymond R. Jones, Mt. Airy, both of Md.

[73 Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

Primary Examiner-James W. Lawrence Assistant Examiner-Marvin Nussbaum Attorney, Agent, or FirmD. Schron [22] Filed: Jan. 26, I973 App]. No.: 327,030

spersive meander line as well as a method and system for employing the variable dispersion characteristics for S 2 4H B ,3 N H 3 3M 2 s 1 B 4 BN 3 7 ,mm R R l 1H3 m 3 31 3 u mTm ""r ""3 w "us .L h I s xp UIF MN 555 56 R i second harmonic signal suppression in amplifier 1 e erences chains. The dispersive characteristics of the disclosed variable dispersion meander line are varied by selectively changing the ratio between the gap spacing of interacting line segments and the pitch of the interact ing line segments. The gap spacing to pitch ratio may be continuously varied within a. desired range while maintaining an acceptable characteristic impedance.

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DISPERSION MEANDER LINE METHOD AND SYSTEM FOR VARYING TI-llE CHARACTERISTICS OF A DISPERSIVE DELAY LINE BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to signal delay lines and, more specifically, to a method and apparatus for selectively varying the phase dispersion characteristic of a meander line and for employing the variable dispersion characteristic to suppress second harmonic power generated in amplifier chains.

2. State of the Prior Art Meander lines are well known and are generally constructed by forming the center strip conductor of a planar stripline transmission line in a pattern which provides a plurality of spaced, generally parallel, electrically interacting segments. The meander line exhibits phase dispersive characteristics in that the total time delay introduced in a signal transmitted along the line is a nonlinear function of the signal frequency.

For example, if two in-phase signals of different frequencies such as first and second harmonic signals are transmitted through a dispersive meander line, the two output signals from the line will be out of phase. The relative phase difference between the two output signals depends upon the dispersive characteristics of the meander line at the frequencies of the applied signals and is a function of the physical configuration of the meander line. Thus, to vary the dispersive characteristics of a meander line at a predetermined frequency, the physical configuration of the line must be varied. Similarly, to retain desired dispersive characteristics of a meander line at different frequencies, the physical configuration of the meander line must be varied.

It may be desirable to vary the dispersive characteristic which a meander line presents to a fixed frequency signal or to retain a particular dispersive characteristic over a range of frequencies. For example, it may be desirable to phase shift a second harmonic signal by a predetermined amount relative to the first harmonic or fundamental signal to achieve second harmonic signal suppression. In an application such as harmonic suppression in a radar system, the fundamental signal frequency may be variable within a predetermined band and, to be effective, the phase dispersion characteristics of the meander line may necessarily have to be variable. Available dispersive meander line signal delay systems cannot provide this capability.

OBJECTS AND SUMMARY OF THE INVENTION It is accordingly an object of the present invention to provide a novel method and system for varying the dispersive characteristics of a phase dispersive delay line.

It is another object of the present invention to provide a novel meander line and method for continuously varying the dispersive characteristics over a desired range while maintaining the characteristic impedance of the line within acceptable limits.

It is yet another object of the present invention to provide a novel method and system for obtaining a desired phase difference between first and second harmonic signals to achieve second harmonic signal cancellation.

These and other objects and advantages are accomplished in accordance with the present invention through the provision of a meander line having a selectively variable physical configuration. More specifically, a first substrate is provided with an electrically conductive strip formed with a plurality of electrically interactive segments or sections along one surface thereof. A second substrate is disposed in at least partially overlying relation with the strip of the first substrate. The second substrate is provided with electrically conducting means contacting the strip of the first substrate for varying the electrical interaction between the segments thereof in response to relative movement between the two substrates.

The interaction varying means is preferably another electrically conductive strip formed with a plurality of electrically interactive segments or sections disposed along the surface of the second substrate. The strip along the surface of the second substrate is preferably substantially a mirror image of the strip along the surface of the first substrate so that the strips are substantially coextensive and coincide in one position of the first substrate relative to the second substrate.

In utilizing the variable disperson meander line for the suppression of second hannonic power in power amplifier chains, an output signal from a signal source such as a first power amplifier is coupled to an amplifier such as a second power amplifier through the variable dispersion line. The output signal from the signal source includes a fundamental frequency component and a second harmonic frequency component, and the dispersive characteristic of the variable dispersion delay line is adjusted to obtain approximately a l phase displacement between the fundamental and second harmonic frequency components. The second harmonic power generated by the second power amplifier is thereby suppressed by the phase shifted second harmonic frequency component of the signal coupled from the signal source to the amplifier.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a perspective view of a prior art dispersive meander line;

FIG. 2A is a graph illustrating the delay characteristics of dispersive and nondispersive delay lines;

FIG. 2B is a graphical representation of typical waveforms of first and second harmonic signals illustrating the effects of transmission through dispersive and nondispersive delay lines;

FIG. 3 is a functional block diagram of a system for suppressing second harmonic signals in accordance with the present invention;

FIG. 4 is an exploded, perspective view of a variable dispersion meander line according to the present invention;

FIGS. 5A and 5B are views in cross-section of the variable dispersion meander line of FIG. 4 illustrating two selected positions thereof;

FIG. 6 is a graph illustrating the phase difference introduced between first and second harmonic signals as a function of the physical characteristics of the variable dispersion meander line of FIG. 4; and,

FIG. 7 is a graph illustrating the variations in characteristic impedance of the variable dispersion meander line of FIG. 4 as a function of the physical characteristics thereof.

DETAILED DESCRIPTION A meander line may typically be utilized in a micro wave system as a delay or phase shifting element. As in FIG. I where a typical meander line is illustrated, an electrically conductive strip may be encapsulated in a substrate 12 of a low loss, microwave dielectric material. The substrate 12 may be any suitable dielectric material having a conductive outer cladding, e.g., copper-clad, Teflon (polytetrafluorethylene)-fiber glass. The conductive strip 10 may be provided with terminals or connectors to a microwave circuit. The strip 10 is configured in a zig-zag or meander line pattern to provide a plurality of spaced, substantially parallel, electrically interactive or coupled phase dispersive segments 16 between the ends 14 thereof. Each segment 16 has length designated L, determined in a conventional manner by the frequency for which the meander line is designed, and a strip width W which, in conjunction with a gap spacing S and an intersegment pitch dimension D, primarily determines the dispersive characteristics of the meander line.

A meander line such as that illustrated in FIG. 1 exhibits a phase dispersive characteristic in that the delay or phase shift introduced between the terminals 14 of the meander line is nonlinear as a function of the frequency of the signal coupled therethrough. This phase dispersive characteristic of a meander line is a function of the physical configuration of the meander line as well as the frequency of the applied signal. For example, as the ratio of the width W of the strip 10 to the pitch D of the interactive segments 16 is increased from zero to one, the phase characteristics vary from nondispersive to resonant. Similarly, the phase dispersion of the meander line is inversely related to the ratio of gap width S to pitch D, i.e., as the ratio S/D decreases, the phase dispersion of the meander line increases.

The dispersive characteristic of a meander line as compared to a nondispersive delay line is illustrated in FIG. 2A. Referring now to FIG. 2A, a linear relationship exists between the frequency of an applied signal expressed in terms of angular frequency w and the electrical length of a nondispersive delay line expressed in terms of relative phase as is indicated by the line 18. Thus, it can be seen that for a nondispersive delay line, a signal having an angular frequency (0 and a signal having an angular frequency 2w will be phase shifted by the same relative amounts because of the linear delay characteristics of a nondispersive delay line at different frequencies.

This linear relationship may be more clearly understood with reference to FIG. 28 wherein a first signal 20 at a fundamental frequency and a signal 22 at the second harmonic thereof are graphically illustrated. With these two signal applied to a nondispersive delay line, each signal is linearly delayed or phase shifted and the phase of the fundamental signal 20 relative to the phase of the second harmonic signal 22 will be the same both before and after the signals are delayed.

A dispersive delay line, on the other hand, exhibits a nonlinear delay for signals of different frequencies and results in the curve 24 of FIG. 2A. Thus, with the same fundamental frequency signal 20 and the same second harmonic signal 22 applied to a dispersive delay line having the characteristic curve 24 illustrated in FIG. 2A, a relative phase shift A will be introduced between the fundamental and second harmonic output signals. This relative phase displacement may be more clearly seen with reference to FIG. 2B.

Referring to FIG. 2B, the fundamental signal 20 and the second harmonic signal 22 may be applied to the phase dispersive meander line of FIG. 1. Assuming that each segment 16 of the meander line of FIG. I exhibits the phase dispersive characteristics illustrated by the curve 24 in FIG. 2A. the output signals from the meander line will have a relative phase displacement NA (where N is the number of segments 16) as is indicated by the phase relationship between the fundamental signal 20 and the nonlinearly delayed second harmonic signal 26 illustrated in phantom in FIG. 28.

It has been found that the nonlinear dispersion characteristic of a meander line is useful in microwave amplifying circuits for the suppression ofsecond harmonic power generated in power amplifier chains. With reference to FIG. 3, for example. a power amplifier 28 may provide a relatively high power microwave output signal having excessive second harmonic signal content. To reduce the second harmonic signal content of the output signal, the output signal from the power amplifier 28 may be applied to a second high power output amplifier 30 through a variable phase dispersion meander line 32 hereinafter described in greater detail.

In operation. the phase relationship between the first and second harmonic signals from the power amplifier 28 may be adjusted through adjustment of the phase dispersion characteristics of the variable phase dispersion meander line 32. When this phase relationship is properly adjusted so that the second harmonic signal is approximately out of phase with the fundamental signal, the second harmonic power generated in the output amplifier 30 may be significantly reduced by the injected, phase shifted second harmonic signal from the variable phase dispersion meander line 32. While, in general, it is necessary to control the amplitude as well as the phase of the injected second harmonic signal to achieve complete cancellation, a significant reduction of more than l0 dB in the second harmonic content of the output amplifier 30 has been demonstrated by adjusting only the phase of the injected harmonic.

The variable phase dispersion meander line 32 of FIG. 3 may be constructed in accordance with the preferred embodiment of the present invention illustrated in FIGS. 4 and 5. Referring now to FIG. 4, the variable phase dispersion meander line 32 of the present invention may include a first substrate 34 having a thickness A and having an electrically conductive strip 36 embedded in one surface 35 thereof. As can be seen more clearly in FIGS. 5A and 5B, the electrically conductive strip 36 is preferably embedded in the substrate 34 sufficiently so that an outer surface of the strip 36 is flush with the surface 35 of the substrate 34.

The strip 36 is desirably configured to provide a plurality of spaced, substantially parallel, electrically interactive phase dispersive segments 36' along the length thereof. As is illustrated in FIG. 5A, the segments 36' may each be defined as having a width W and may be separated by a gap separation distance S. The separation distance S plus the width W may define a distance D (the pitch dimension) between corresponding edges of the segments 36', e.g., between the rightmost or leftmost edges of the segments 36'.

A second substrate 38 having an electrically conductive strip 40 embedded in and flush with one surface 37 thereof may provide a means for varying the phase dispersive characteristics of the segments 36' embedded in the first substrate 34. The electrically conductive strip 40 is preferably configured as a mirror image of the strip 36 with an identically formed plurality of electrically interactive, phase dispersive segments 40' along the length thereof. With the surfaces 35 and 37 of the respective substrates 34 and 38 disposed in abutting relation as is illustrated in FIG. 5A, the conductive strips 36 and 40 are disposed in electrical contact and thus provide an electrically continuous, substantially coextensive strip. By moving one of the substrates 34 and 38 relative to the other as is illustrated in FIG. 5B, the ratio of S/D may be varied to vary the dispersion characteristics of the meander line.

While the segments 48' are preferably formed from an electrically continuous strip 48, it can be seen that the portions of the strip 40 connecting the segments 40' do not directly affect the S/D ratio when the substrates 34 and 38 are relatively moved. Thus, the segments 40 need not be electrically connected to obtain a movement responsive variation in the S/ D ratio and thus the phase dispersive characteristics of the meander line. The illustrated embodiment is, however, preferred since losses due to sharp corners are minimized with the illustrated embodiment.

The substrates 34 and 38 may be formed from a suitable low loss, microwave dielectric material such as commercially available composite of copper-clad, Teflon (polytetrafluorethylene)-fiber glass. The conductive strips 36 and 40 may be formed from any suitable, highly electrically conductive material, preferably copper with a gold plating thereover. Moreover, the corners of the transmission line formed by the conductive strips 36 and 40 may be chamfered as illustrated to reduce reflections.

With continued reference to FIG. 4, the substrates 34 and 38 may be accurately slidably positioned relative to each other for the purpose of accurately varying the dispersion characteristics of the meander line by slidably mounting one of the substrates, e.g., the substrate 38, in a support frame generally indicated at 42. The support frame 42 may include a relatively flat support plate 44 having a transversely extending flange 46 at one end thereof and spacing members 48 along each edge thereof. The spacing members 48 may be substantially identical in thickness to the thickness A of the substrate 38 and may slidably receive the substrate 38 therebetween with a surface 50 of the substrate 38 resting in abuttment with a surface of the support plate 44.

A laterally extending flange 52 may be provided at one end of the substrate 38, and threaded apertures generally indicated at 54 and 56 may be provided through the respective flanges 46 and 52. A threaded adjustment screw 58, for example a machine screw threaded in opposite directions at opposite ends thereof, may be threaded into the threaded apertures 54 and 56 to provide accurate movement of the substrate 38 along the channel formed by the spacers 48 in response to rotation of the adjustment screw 58. The substrate 34 may then be conventionally fastened to the support frame 42 so that the substrate 34 is fixed relative to the support frame 42. For example, threaded apertures 60 may be provided in the spacers 48 and correspondingly positioned apertures 62 may be provided through the substrate 34. The substrate '34 may thereby be bolted to the spacer 48 so that the surfaces 35 and 37 of the substrates 34 and 38 are in sliding engag'ement.

In operation, the substrates 34 and 38 of the variable dispersion meander line of FIG. 4 may be initially positioned so that the strips 36 and 40 are substantially coextensive in width as is illustrated in FIG. 5A. To facilitate an understanding of the invention, it may be assumed that the variable dispersion meander line is to be employed to reduce the second harmonic signal content of an amplified signal as was previously described in connection with FIG. 3. In this connection, an amplified microwave signal from a first power amplifier may be applied through the variable dispersion meander line of FIG. 4 and the output signal therefrom may be applied to a second power amplifier. The output signal from the second power amplifier may be monitored for second harmonic signal content and the relative positions of the substrates 34 and 38 may be adjusted by turning the adjusting screw 58.

As the adjusting screw 58 is rotated, the substrates 34 and 38 and the electrically interactive segments 36' and 40' move relative to each other resulting in a change in the 5/0 ratio and the dispersive characteristics of the meander line. As is illustrated in FIG. 6, the phase delay of the fundamental signal relative to its second harmonic signal for each electrically interactive segment of the variable dispersion meander line may be nonlinearly varied over a relatively large range by changing this S/D ratio.

With continued reference to FIG. 6, the phase difference Ad) for various ratios of substrate thickness 2A to coupled segment pitch D varies in a decreasing manner with an increase in the ratio of S/ D. Thus, for a ratio of 2A/D 2.0 (curve 66) the phase difference Aqb for each interacting segment of the variable dispersion meander line may be varied between approximately 35 and by varying the ratio of S/D between 0.5 and 0.01. Similarly, curves 68 and 70 indicate the variable phase dispersion characteristics obtained in accordance with the present invention for ratios of 2A/D equal, respectively, to 1.0 and 0.5.

A 180 phase difference between the fundamental and the injected second harmonic signals ordinarily provides maximum second harmonic signal cancellation. Thus, with a variable dispersion meander line having the characteristics illustrated by the curve 66 of FIG. 6, three interacting segments may be provided to permit a variation of phase difference over a range of between and 270, i.e., three times the quantity 2A/D for one meander line section. The S/D ratio may then be varied within this range by adjusting the screw 58 to provide a total of 180 phase displacement between the first and second harmonic signals. In the exemplary meander line having the characteristics illustrated by the curve 66, this S/D ratio is approximately 0.15 since this ratio provides a phase difference Ad) of approximately 60 for each of the three interacting segments.

The practical range over which the ratio S/D may be varied is determined by the variation in characteristic impedance which can be tolerated in the particular application of the variable dispersion meander, line. As the S/D ratio is varied, the characteristic impedance of the variable dispersion meander line varies and may result in an undesirable loss of power should too great an impedance mismatch result from varying the S/D ratio.

In FIG. 7 the variation of the characteristic impedance Z of a variable dispersion meander line constructed in accordance with the teachings of the present invention is illustrated as a function of the ratio 8/ D for ratios of 2A/D equal to 2.0 (curve 72), 1.0 (curve 74) and 0.5 (curve 76). Referring now to FIG. 7 wherein the product of the characteristic impedance Z times the square root of the relative dielectric constant V? of the substrate material is plotted as a function of the ratio S/D, it can be seen that for a ratio of 2A/D 2.0 (curve 72), the characteristic impedance-relative dielectric constant product may vary from approximately 46 ohms at an S/D ratio of 0.01 to approximately 130 ohms at an S/D ratio of 0.5. It can be seen that with the exemplary meander line previously discussed in connection with FIG. 6 adjusted to an S/D ratio of 0.15, the characteristic impedance-relative dielectric constant product is approximately 80 ohms.

Assuming that a typical substrate material has a relative dielectric constant of about three, the characteristic impedance of the variable dispersion meander line having a 2A/D ratio of 2.0 is approximately 46 ohms when adjusted to provide an S/D ratio of 0.15 and the resultant 180 fundamental to second harmonic phase difference. In a circuit application wherein the characteristic impedance must be maintained within certain acceptable limits, e.g., 50 ohms :10 ohms, this value of 46 ohms is well within the acceptable limits at the S/D ratio of 0.15 and permits adjustment on either side of the 0.15 S/D ratio.

It can be seen from the foregoing description that the variable dispersion meander line of the present invention may provide a continuously variable dispersion characteristic within desired limits while substantially maintaining the characteristic impedance of the line within an acceptable range.

The disclosed variable phase dispersion technique may be readily adapted for use in harmonic cancellation in microwave systems and can be applied to other systems wherein phase equalizers or variable time delay devices are employed.

The present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed is:

l. A variable delay line comprising:

a first substrate having a first electrically conductive strip embedded in one surface thereof, said first strip being configured to provide a plurality of spaced, electrically interactive, phase dispersive segments along the length thereof; and, second substrate overlying at least a portion of the one surface of said first substrate and including electrically conductive means electrically contacting said first strip for varying the spacing between said dispersive segments to thereby vary the electrical interaction between the segments of said first strip responsively to relative movement between said first and second substrates.

2. The variable delay line of claim 1 wherein said spacing varying means comprises a second electrically conductive strip including a plurality of electrically interactive, phase dispersive segments embedded in the surface of said second substrate overlying the one sur face of said first substrate, the segments of said second strip being configured to coincide with and electrically contact associated ones of the segments of said first strip in one position of said second substrate relative to said first substrate.

3. The variable delay line of claim 1 wherein each of said spacing segments of said first strip have a width W and are spaced by a distance S. said electrical interaction varying means being operable to vary the ratio of the spacing S to the distance S+W in response to said relative movement.

4. A variable delay line comprising:

a first substrate having a first electrically conductive strip embedded in one surface thereof. said first strip being configured to provide a plurality of spaced, electrically interactive. phase dispersive segments along the length thereof. each of said electrically interacting segments of said first strip having a width W and being spaced by a distance S; and,

a second substrate overlying at least a portion of the one surface of said first substrate and including means electrically contacting said first strip for varying the electrical interaction between the segments of said first strip responsively to relative movement between said first and second substrates, said electrical interaction varying means comprising a second electrically conductive strip including a plurality of electrically interactive. phase dispersive segments embedded in the surface of said second substrate overlying the one surface of said first substrate, the segments of said second strip being configured to coincide with and electrically contact associated ones of the segments of said first strip in one position of said second substrate relative to said first substrate, said electrical interaction varying means being operable to vary the ratio of the spacing S to the distance S+W in response to said relative movement.

5. Apparatus comprising:

a first member;

first electrically conductive means configured for mutual electrical interaction between spaced segments thereof and carried by said first member;

first and second terminals connected to said electrically conductive means;

a second member;

second electrically conductive means carried by said second member in electrically interacting and slidably contacting relationship to said first electrically conductive means; and,

means for moving said first member relative to said second member. said second electrically conductive means being configured to vary the spacing between the segments of the first electrically conductive means in response to the relative movement caused by said moving means to thereby vary the electrical interaction of said first and second members and in turn the effects of said first electrically conductive means on a signal passed between said first and second terminals.

6. The apparatus of claim 5 wherein first and second electrically conductive means are each substantially planar and are carried respectively by said first and second members in sliding contact with each other.

members.

8. The method of claim 7 wherein the effective physical configuration of the meander line is varied by slidably contacting each of the electrically interactive strips of the meander line with a substantially coextensive electrical conductor and physically displacing one of the electrical conductor and the strips relative to the other. 

1. A variable delay line comprising: a first substrate having a first electrically conductive strip embedded in one surface thereof, said first strip being configured to provide a plurality of spaced, electrically interactive, phase dispersive segments along the length thereof; and, a second substrate overlying at least a portion of the one surface of said first substrate and including electrically conductive means electrically contacting said first strip for varying the spacing between said dispersive segments to thereby vary the electrical interaction between the segments of said first strip responsively to relative movement between said first and second substrates.
 2. The variable delay line of claim 1 wherein said spacing varying means comprises a second electrically conductive strip including a plurality of electrically interactive, phase dispersive segments embedded in the surface of said second substrate overlying the one surface of said first substrate, the segments of said second strip being configured to coincide with and electrically contact associated ones of the segments of said first strip in one position of said second substrate relative to said first substrate.
 3. The variable delay line of claim 1 wherein each of said spacing segments of said first strip have a width W and are spaced by a distance S, said electrical interaction varying means being operable to vary the ratio of the spacing S to the distance S+W in response to said relative movement.
 4. A variable delay line comprising: a first substrate having a first electrically conductive strip embedded in one surface thereof, said first strip being configured to provide a plurality of spaced, electrically interactive, phase dispersive segments along the length thereof, each of said electrically interacting segments of said first strip having a width W and being spaced by a distance S; and, a second substrate overlying at least a portion of the one surface of said first substrate and including means electrically contacting said first strip for varying the electrical interaction between the segments of said first strip responsively to relative movement between said first and second substrates, said electrical interaction varying means comprising a second electrically conductive strip including a plurality of electrically interactive, phase dispersive segments embedded in the surface of said second substrate overlying the one surface of said first substrate, the segments of said second strip being configured to coincide with and electrically contact associated ones of the segments of said first strip in one position of said second substrate relative to said first substrate, said electrical interaction varying means being operable to vary the ratio of the spacing S to the distance S+W in response to said relative movement.
 5. Apparatus comprising: a first member; first electrically conductive meanS configured for mutual electrical interaction between spaced segments thereof and carried by said first member; first and second terminals connected to said electrically conductive means; a second member; second electrically conductive means carried by said second member in electrically interacting and slidably contacting relationship to said first electrically conductive means; and, means for moving said first member relative to said second member, said second electrically conductive means being configured to vary the spacing between the segments of the first electrically conductive means in response to the relative movement caused by said moving means to thereby vary the electrical interaction of said first and second members and in turn the effects of said first electrically conductive means on a signal passed between said first and second terminals.
 6. The apparatus of claim 5 wherein first and second electrically conductive means are each substantially planar and are carried respectively by said first and second members in sliding contact with each other.
 7. A method of selectively varying between predetermined limits the phase dispersive characteristics of a meander line having electrically interactive, spaced conductive strips comprising the steps of nondestructively varying the effective physical configuration of the meander line by slidably contacting the interactive conductive strips with electrically conductive members and simultaneously varying the width of each electrically interactive strip while varying the spacing therebetween by moving the strips relative to the conductive members.
 8. The method of claim 7 wherein the effective physical configuration of the meander line is varied by slidably contacting each of the electrically interactive strips of the meander line with a substantially coextensive electrical conductor and physically displacing one of the electrical conductor and the strips relative to the other. 